I took both Phoebe and Chloe outside to fly yesterday, and things were worse than ever; both struggled to get off the ground. To be honest it was so bizarre it was almost comical. It couldn’t possibly be sensor drift so perhaps it’s the battery?
A very little bit of research (i.e. googling) soon showed LiPo batteries are intended to work above 20°C and their internal resistance rises significantly as the temperature drops below that point. That would explain why the 3S (11.1v) LiPos run so well during the summer, but seem powerless now in the colder side of Autumn.
So I wrapped Phoebe’s battery up in bubble wrap and took her outside again this morning; normal behaviour has resumed; it seems that even LiPo batteries needs a snuggly down duvet in winter to keep them warm.
I’ve got a self-adhesive neoprene rubber sheet on order from ebay to wrap around my batteries now; these’ll be my winter batteries, and I’ll leave a couple unwrapped for summer use. I’ve also bought an IR temperature gun so I can be more scientific and less speculative about the temperature the battery is running at.